1. Field of the Invention
The invention pertains generally to ambient air, soil, and water temperature sensing and reporting instrumentation. More specifically, the invention discloses an assembly of temperature sensor modules specially adapted for repeated and prolonged use in harsh outdoor, underground and underwater conditions, especially at low ambient temperatures (i.e. to at least −40 degrees C./F.), and designed to resist damage from mechanical stresses arising from actions on the assembly such as flexure, twisting, kinking, and tension. The invention can be provided with a standard format electrical connector for electrical association with a separate external device via a signal cable. Alternatively the invention can utilize available wireless digital communication technology to operate without hard wire connections. The temperature sensors can be placed at any position along the signal cable.
The preferred embodiment of the invention features encapsulated sensor modules with integral strain relief and robust environmental protection. The materials and methods of construction offer superior extreme low temperature performance (i.e. to at least −40 degrees C./F.) and enable the sensor elements to tolerate more coil and uncoil cycles than the prior art.
2. Background
The short cool summers and long cold winters that typify the climatic conditions found at high latitudes are conducive to the formation of permafrost or perennially frozen ground. Climatic conditions at very high latitudes also result in seasonal and multiyear ice formations on many lakes and offshore (marine) environments. Permafrost soils present unique design and construction challenges in cold regions around the world for a broad range of projects including community housing, schools, utilities, roads and bridges, airports, resource development, and defense. The occurrence of freshwater ice on inland water bodies and sea ice in the offshore realm also has ongoing relevance to commercial and academic interests focused on resource development and transportation.
Continuous records of accurate ground temperature data highly resolved with depth are required for engineering, construction, and scientific purposes on a regional, local and site specific basis. The invention addresses a need to improve the reliability and performance over previous art while achieving user cost reductions.
3. Description of Prior Art
The prior art has been known and widely used for at least three decades. The prior art accomplishes temperature measurement using a plurality of analog sensors mounted on dedicated circuits within a multiconductor signal cable. The analog sensors typically consist of thermistors, temperature sensitive resistors, which exhibit a temperature dependent resistance. A separate conductor within a cable must be allocated to each sensor although multiple sensors of this type can share a common ground. DC resistance is the measured parameter for this type of sensor. Measurements are typically accomplished in the field by connecting the leads from a conventional test meter to one dedicated circuit at a time and manually recording resistance values. Often a manual switching device is used between the test meter and multiconductor cable to improve the quality of the connections and speed of the procedure. Generic automated analog polling and data logging devices have also been used in cases where relatively few sensors are installed on a long-term basis such as under buildings or remote land-based or sea-based monitoring stations. The measured resistance is later converted to a temperature using the Hart-Steinhardt Equation with appropriate input parameters for the specific thermistor employed.
The use of thermistors for several decades has led to general acceptance of the methodology for obtaining multipoint temperature data as well as incremental improvements to the art. However, inherent limitations to the prior art persist. The signal cable must possess a separate conductor for each analog sensor plus one additional conductor to be used for ground. For applications that require many sensors, specialty signal cable with an unusually large number of conductors or more than one smaller multiconductor cable must be used to provide the required dedicated circuits. The use of cables with high numbers of conductors also increases manufacturing costs, and the cost of maintenance and repair. Large cables also tend to be heavy and inflexible for the end user who must carry, deploy, and recover the cables multiple times. The installation of analog sensors within a cable is typically completed using heat sensitive shrink materials which frequently form an unreliable seal with the outer jacket material and introduce areas of concentrated bending stress on either side of the splice area. Cold temperature failures of the outer cable jacket are common.
The invention possesses numerous benefits and advantages over known multipoint temperature sensing cables for cold regions. In particular, the invention utilizes an established digital communication protocol to reduce the number of required conductors within a cable, thereby affording lower weight and increased flexibility to the user.